1. Field of the Invention
This invention relates to a semiconductor device and a method of producing the same, and particularly to a semiconductor device for pressure sensor with an integrated circuit and a method of the same.
2. Description of the Prior Art
Semiconductor devices for detecting a pressure with a diaphragm formed by electrochemical etching are known. U.S. Pat. Nos. 5,360,521, 5,525,549, and Japanese patent application provisional application No. 6-45618 disclose this type of semiconductor devices.
More specifically, a semiconductor wafer is prepared which includes a first semiconductor layer (p type silicon layer) having a first conductivity and a second semiconductor layer (n type silicon layer with a second conductivity laminated with the first semiconductor layer. Next, an integrated circuit is formed for each chip unit on the semiconductor wafer. Next, a diaphragm is formed by electrochemical etching at each chip unit. Then, the semiconductor wafer is cut along scribe lines to provide the semiconductor chips.
During this process, on a surface of the semiconductor wafer, a wire of A1 or the like is formed for electrochemical etching at each chip unit. The first semiconductor layer is partially removed to form a hollow portion to provide the diaphragm by applying a voltage to the wire to effect the electrochemical etching.
In each chip unit, impurity diffusion layers, such as a p+ impurity diffusion layer, are formed to isolate respective elements in the integrated circuit from each other. The impurity diffusion layer is formed so as to pierce the second semiconductor layer from the surface of the second semiconductor layer opposite to the first semiconductor layer to the surface of the first semiconductor layer contacting the second semiconductor layer.
In these prior arts, the wire for electrochemical etching crosses the impurity diffusion layer. Here, although, the wire is electrically insulated from the impurity diffusion layer with an insulation film such as an oxide film, the wire may short-circuit with the impurity diffusion layer at a crossing point during electrochemical etching because of defects inherently existing the insulation film or the like.
More specifically, during the electrochemical etching, the wire is supplied with a voltage to provide reverse-bias between the first and second semiconductor layers to conduct the etching in the first semiconductor layer. When a current in the wire rapidly increases, etching is finished.
If the wire short-circuits with the impurity diffusion layer at a crossing point or an overlapping point, the current leaks from the wire to the first semiconductor layer through the impurity diffusion layer. Then, the etching is finished at timing of leakage, so that the desired etching cannot be provided.
Thus, it is required to provide a semiconductor device having a diaphragm for pressure detection and an integrated circuit with a structure or a method for preventing short circuit from the etching wire to the first semiconductor layer through the impurity diffusion layer during electrochemical etching.